Ignition control system and method

ABSTRACT

The invention is directed to an ignition control system that dynamically adjusts the warm-up time of an igniter within a predetermined range depending on the success or failure of the previous ignition or start-up cycle. The system activates the igniter and waits a predetermined or computed warm-up time. At the end of the warm-up time, the system opens a gas valve. The system then waits a preset time from the opening of the gas valve to determine whether ignition was successful or not. If the ignition was successful, the system computes a new igniter warm-up time by decrementing the current time and stores this new value for use during the next start sequence. If the ignition was unsuccessful, the system computes a new warm-up time by incrementing the current value and retrying the start sequence. Preferably, a successful ignition is always determined by checking for the presence of flame a fixed time following the opening of the gas valve.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to furnaces and, more specifically, to ignition control systems for use with furnaces.

[0003] 2. Background Information

[0004] Furnaces and other fuel-based appliances typically include a fuel control system for supplying and controlling the flow of fuel, e.g., natural gas, to the furnace and for starting, i.e., igniting, that fuel to produce heat. A fuel control system includes a burner, a valve for controlling the flow of fuel to the burner and an igniter for igniting the fuel provided to the burner. Most igniters are electrical resistance type igniters, and a power source is applied across the igniter causing it to heat up.

[0005] Typically, the igniter is electrically energized for a predetermined time period, sometimes referred to as the igniter warm-up time, to enable it to reach a temperature sufficiently high enough to ignite the fuel. There are several manufacturers of igniters used in such systems. An igniter from any one manufacturer, because of its particular material composition, mass, and physical configuration and properties, will generally heat up at a different rate and to a different final temperature than an igniter from another manufacturer. Even the same model igniters from the same manufacturer can have significantly different warm-up rates and final temperatures. Furthermore, the time it takes a given igniter to warm-up to a sufficient temperature changes over the life of the igniter.

[0006] When it is known that a particular igniter having a fast warm-up time will be used, the length of the igniter warm-up time period can be established at a relatively low value, for example, at 15 seconds. However, when the particular igniter to be used has a slow warm-up time or it is desirable that the system is to be usable with either fast or slow warm-up time igniters, the length of the igniter warm-up time period is established at a relatively large value, for example, at 45 seconds. The use of such a long warm-up time, however, can reduce the life of many igniters which do not require such lengthy warm-ups. It also increases the electrical power consumption of the furnace, thereby resulting in added operational costs. Accordingly, a fuel control system that minimizes igniter warm-up time and yet still starts the furnace or appliance successfully is desirable.

[0007] U.S. Pat. No. 5,364,260 to Moore discloses a microcomputer-driven igniter system in which the microcomputer is programmed to generate a unique igniter warm-up time for use during each burner start cycle. The microcomputer of the '260 patent determines the time it takes from when the fuel valve is opened to when flame is first detected at the burner. If the ignition attempt is successful, the igniter warm-up time is reduced during the next burner cycle based on a decrease in the length of the flame detecting time period for the current burner cycle over the length of the flame detecting period on a previous burner cycle. If the igniter doesn't ignite the fuel during a so-called valve trial time period, the flow of fuel to the burner is terminated and there is a lock-out until manual resetting of the system takes places. The igniter warm-up time period is increased when a second event occurs, such as a lapsing of a pre-determined number of burner cycles which can be coupled to an increase in the length of the flame detecting time period.

SUMMARY OF THE INVENTION

[0008] Briefly, the invention relates to an ignition control system that dynamically adjusts the warm-up time of an igniter within a predetermined range depending on the success or failure of the previous ignition or start-up cycle. The system, which is preferably utilized in a furnace, includes a microprocessor coupled to an electrical programmable read only memory (EPROM) configured to store a series or program instructions relating to an ignition sequence to be executed by the microprocessor. The furnace includes a burner in which the igniter is disposed, an inducer motor for delivering combustion air to the burner, and a fuel valve for selectively providing fuel to the burner. The microprocessor is coupled to and controls the inducer motor, the igniter and the fuel valve. It may also receive signals from one or more sensors, such as a flame sensor positioned to detect the presence or absence of flame at the burner, and one or more pressure and/or limit switches for confirming the flow of air through the furnace and the absence of an over-temperature condition.

[0009] In response to a call for heat, the microprocessor accesses and executes the program instructions stored at the EPROM. In particular, it activates the igniter causing it to warm-up. It may also run the inducer motor, thereby forcing any residual or leftover combustible materials out of the furnace. At the end of a first predetermined igniter warm-up time, e.g., 30 seconds, the microcontroller opens the fuel valve, thereby causing fuel to be delivered to the burner, which, in turn, directs the fuel to the hot igniter. At a first preset time following the opening the fuel valve, e.g., 3 seconds, the microcontroller deactivates the igniter. The microprocessor then waits a second preset time following the opening of the fuel valve, e.g., 5 seconds, to check the flame sensor and see whether flame is present, thereby indicating a successful or unsuccessful ignition.

[0010] If the ignition sequence was successful, the microprocessor decreases or decrements the igniter warm-up time by a certain amount, e.g., 3, 6, 12 or 24 seconds, during the next furnace start. This process is repeated at each start and, assuming ignition is successful each time, the igniter warm-up time continues to be decremented until a minimum warm-up time is reached, e.g., 6 seconds. If, during any furnace start, ignition is unsuccessful, i.e., flame is not present after waiting the second preset time, the microprocessor increases the igniter warm-up time by a certain amount, e.g., 3, 6, 12 or 24 seconds, and retries the ignition sequence. The warm-up time can be increased up to a maximum warm-up time, e.g., 54 seconds. If ignition is continues to be unsuccessful after some number of tries at the maximum warm-up time, the microprocessor enters a “lock-out” mode in which start-up of the furnace is blocked for a preset time interval.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The invention description below refers to the accompanying drawings, of which:

[0012]FIG. 1 is a highly schematic partial block diagram of a furnace including the ignition control system of the present invention;

[0013] FIGS. 2A-B is a flow diagram of a preferred method of the present invention; and

[0014] FIGS. 3-5 are flow diagrams of alternative methods in accordance with the present invention.

DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT

[0015]FIG. 1 is a block diagram of an ignition control system 100 in accordance with the present invention. System 100 includes a controller 102 having a microprocessor (μp) 104 and a memory 106, such as an electrically programmable read only memory (EPROM). As described herein, memory 106 stores program instructions executable by the microprocessor 104. Controller 102 may also include a port 108, such as a RS-232 port, which can be used to modify or change the program instructions stored at memory 106. System 100 further includes a burner 110, which receives fuel from a gas line 112, a gas valve 114 disposed in the gas line 112, and an igniter 116. Burner 110, gas valve 114 and igniter 116 are each operatively controlled by the controller 102. In particular, the gas valve 114 is moveable between a closed and an open position, thereby selectively controlling the supply of gas to the burner 110. The igniter 116 is disposed proximate to the burner 110 so as to ignite fuel therefrom. System 100 also includes a flame sensor 118, which is configured to detect the presence of a flame from the burner 110, and to report that condition to the controller 102. System 100 may further include an inducer blower motor 122 for providing combustion air to the burner 110, and one or more pressure and/or limit switches, such as pressure switch 124 and limit switch 126, for providing furnace operational information to the controller 102. A thermostat 120 is also included for providing calls, such as a call for heat, to the controller 102.

[0016] Controller 102 is preferably a printed circuit board having a plurality of interconnected components. Suitable components, such as microprocessors and/or EEPROMs, for use with the present invention are commercially available from Microchip Technology Inc. of Chandler, Ariz. and Motorola Inc. of Schaumburg, Ill., among others.

[0017] When the space being heated falls below a preset temperature, the thermostat 120 issues a call for heat signal to the controller 102, which responds by activating the furnace. As part of the furnace activation process, the controller 102 runs the inducer blower motor 122 for some time, e.g., 30 seconds, to force any residual combustion products out of the furnace. The controller 102 also confirms that the pressure switch 124 is open, thereby confirming that the inducer blower is operating properly, and that the limit switch 126 is closed, thereby confirming that an over-temperature condition does not exist. Assuming the pressure and limit switches indicate proper operation of the furnace, the controller 102 energizes the igniter 116 for a predetermined warm-up time. The controller 102 then opens the gas valve 114 delivering fuel to the burner 110. The fuel is then ignited by the hot igniter 116. In accordance with the present invention, the controller 102 dynamically modifies and/or adjusts the amount of time that the igniter 116 is warmed up each time the furnace is activated so as to prolong the life of the igniter 116 and yet still achieve a successful ignition of the furnace.

[0018]FIG. 2 is a flow diagram of a preferred method in accordance with the present invention. The control system 100 initially remains in a suspended state waiting for a call for heat from the thermostat 120, as indicated at block 202. Upon receiving a call for heat, the controller 102 runs the inducer blower motor 122 for sufficient time to force residual combustion materials, if any, out of the furnace, as indicated at block 204. The controller 102 then checks the status of the pressure and limit switches 124, 126 to confirm that the inducer blower is operating properly and that the furnace is not in an over-temperature condition, as indicated at block 206. If so, the controller 102 energizes the igniter 116, as indicated at block 208, and waits a predetermined or computed igniter warm-up time, as indicated at block 210. For the first or initial start of the furnace, the predetermined igniter warm-up time is approximately 30 seconds. At the end of the igniter warm-up time, the controller 102 opens the gas valve 114, as indicated at block 212. The controller 102 then de-energizes the igniter 116 after a first preset time following the opening the gas valve 114, e.g., approximately 3 seconds, as indicated at block 214. Next, the controller 102 waits a second preset time also following the opening of the gas valve 114, e.g., approximately 5 seconds, and checks to see if a flame is present, as indicated at block 216. Specifically, the controller 102 checks the signal from the flame sensor 118 at the expiration of the second preset time.

[0019] Based on the presence or absence of a flame at the expiration of the second preset time, the controller 102 makes a determination as to whether or not there has been a successful ignition by the burner 110, as indicated by decision block 218. That is, if a flame is determined to be present upon the expiration of the second preset time, the controller 102 concludes that ignition was successful. In response to a successful ignition, the controller 102 determines whether the igniter warm-up time is already set to a preset minimum warm-up time, e.g., six seconds, as indicated by decision block 220. In this case, the response is No, as the initial igniter warm-up period was 30 seconds, as described above. As a result, in this case, the controller 102 computes a new igniter warm-up time for use during the next start cycle, as indicated at block 222. In particular, the controller 102 decreases the current igniter warm-up time, i.e., 30 seconds, by a preset downward increment or step, e.g., three seconds. In other words, the microprocessor 104 computes a new igniter warm-up time as follows: 30−3=27 seconds, and stores this new warm-up time at for use during the next start cycle of the furnace, as also indicated at block 222. The new warm-up time may be stored at memory 106, or at some other memory, such as a register or a random access memory (RAM). Processing then returns to the wait state represented by block 202, as shown by arrow 221.

[0020] During the next start cycle, steps 202-216 are repeated, although this time the igniter is only energized for 27 seconds at block 210 before the controller 102 opens the gas valve 114. If ignition is again successful, the warm-up time is again reduced by the preset increment, e.g., three seconds, at block 222, in this case, to a value of 24 seconds, and this new value is stored for use during the next start cycle. The new value, e.g., 24 seconds, replaces the previous value, e.g., 27 seconds. For example, the memory location may be overwritten with the new value. This process is repeated, assuming ignition is successful each time, until the igniter warm-up time is reduced to the preset minimum, e.g., six seconds. At this point, the result of decision block 220 is yes and processing simply returns to the wait state of block 202 without making any further changes to the igniter warm-up time. That is, the controller 102 (FIG. 1) does not reduce the warm-up time below the preset minimum, e.g., six seconds.

[0021] After each successful ignition, the controller 102 preferably increments a counter so as to keep track of the number of furnace starts.

[0022] If, during any start cycle including the initial start, ignition is unsuccessful, i.e., no flame is detected after waiting the second preset time following the opening of the gas valve 114, then processing moves from decision block 218 via No arrow 219 to block 224 (FIG. 2B). Here, the controller 102 determines whether the current start cycle is the furnace's initial cycle, i.e., the first start of the furnace. If it is not, the controller 102 then determines whether the current igniter warm-up time is set to a preset maximum warm-up time, e.g., 54 seconds, as indicated by No arrow 225 leading to decision block 226. If the current warm-up time is less than the preset maximum, the controller 102 computes a new igniter warm-up time for use during a retry, as indicated at block 228. In particular, the controller 102 increases the current igniter warm-up time by a preset upward increment or step, e.g., 3 seconds. The new warm-up time is also stored. Using this new warm-up time, the ignition sequence, i.e., steps 204-216, are repeated as indicated by block 230, and the controller 102 determines whether ignition was successful on this retry, as indicated by decision block 232. If so, the controller 102 next determines whether the furnace has been started a total of 250 times or less, as indicated at decision block 234. If so, the controller uses the current warm-up time during the next start cycle, as indicated at block 236, and checks for successful ignition, at decision block 232.

[0023] By virtue of block 226, the ignition control system 100 limits the igniter warm-up time to a preset maximum value, e.g., 54 seconds. Accordingly, the warm-up time can range between the preset minimum, e.g., six seconds, and the preset maximum, e.g., 54 seconds. With each successful start, the warm up time is reduced preferably in three second increments or steps down to the minimum of six seconds. And, with each failed start, the warm-up time is increased preferably in three second increments or steps up to the maximum of 54 seconds.

[0024] Returning to decision block 224 (FIG. 2B), if the failed ignition occurred on the initial start of the furnace, the controller 102 repeats the start sequence, i.e., steps 204-216, using the predetermined warm-up time, e.g., 30 seconds, as indicated at block 230. The controller 102 preferably maintains a counter that is incremented for each consecutive ignition failure. If ignition is still unsuccessful, the controller 102 determines whether the number of consecutive ignition failures is equal to or less than a preset limit, e.g., five, as indicated by decision block 238. If so, processing returns via Yes arrow 239 to decision block 224. If the controller 102 is unable to start the furnace after six consecutive retries, it enters a lock-out state, as indicated by block 240. During the lock-out period, e.g., 1 hour, the controller 102 is prevented from trying to start the furnace. At the end of the lock-out period, the controller returns to the wait state as represented by block 202 (FIG. 2A).

[0025] Upon entering the lock-out state, the controller 102 may activate a diagnostic indicator, such as a set or row of LEDs, to notify service personnel of the particular type of failure or error condition.

[0026] Referring to decision block 234, if the furnace has been successfully started over 250 times with the current warm-up time, the controller 102 computes a new igniter warm-up time by decreasing the current warm-up time by the preset downward increment, e.g., three seconds, as indicated by No arrow 235, which returns processing to block 222 (FIG. 2A). The controller 102 then returns to the wait state represented by block 202.

[0027] It should be understood that the maximum and minimum warm-up times and the upward and downward increments or steps, e.g., three seconds, can be modified and still achieve the objectives of the present invention. Indeed, by using port 108, a service technician can reprogram the instructions steps as well as the maximum, minimum and increment or step values stored at memory 106, thereby tuning the ignition sequence performed by the controller 102.

[0028]FIGS. 3A and 3B are a flow diagram of an alternative start cycle implemented by the controller 102. The steps of blocks 302-316 (FIG. 3A) correspond to the steps of blocks 202-216 of FIG. 2A described above. Based on the presence or absence of a flame at the expiration of the second preset time, the controller 102 makes a determination as to whether or not there has been a successful ignition of the burner 110, as indicated by decision block 318. That is, if a flame is determined to be present upon the expiration of the second preset time, the controller 102 concludes that ignition was successful. In response to a successful ignition, the controller 102 determines whether the igniter warm-up time is set to a preset minimum, which, in is this embodiment, is preferably twelve seconds, as indicated by decision block 320. In this case, the response is No as the initial igniter warm-up period was 30 seconds. As a result, the controller 102 computes a new igniter warm-up time for use during the next start cycle, as indicated at block 322. In particular, the controller 102 decreases the current igniter warm-up time, i.e., 30 seconds, by a preset downward increment, e.g., three seconds. In other words, the microprocessor 104 computes a new igniter warm-up time as follows: 30−3=27 seconds, and stores this new warm-up time for use during the next start cycle of the furnace, as also indicated at block 322. As indicated by arrow 323, processing then returns to the wait state represented by block 302.

[0029] During the next start cycle, steps 302-316 are repeated, although this time the igniter is only energized for 27 seconds at block 310 before the controller 102 opens the gas valve 114. If ignition is again successful, the warm-up time is reduced by another downward increment, e.g., three seconds, at block 322, to a value of 24 seconds, and this new value is stored for use during the next start cycle. This process is repeated, assuming ignition is successful each time, until the igniter warm-up time is reduced to the preset minimum, e.g., twelve seconds. At this point, the result of decision block 320 is yes and processing simply returns to the wait state of block 302 without making any further changes to the igniter warm-up time as indicated by Yes arrow 321 leading to block 302. Thus, a minimum warm-up time, which, in this embodiment, is preferably twelve seconds, is established.

[0030] After each successful ignition, the controller 102 preferably increments a counter so as to keep track of the number of furnace starts.

[0031] If, during any start cycle including the initial start, ignition is unsuccessful, i.e., no flame is detected after waiting the second preset time following the opening of the gas valve 114, then processing moves from decision block 318 to block 324 (FIG. 3B). Here, the controller 102 determines whether the failed ignition occurred during a first or second retry. If not, i.e., if the failed ignition is a third retry, the controller 102 then determines whether the current igniter warm-up time is set to a preset maximum value, e.g., 36 seconds, as indicated by decision block 326. If it is not, the controller 102 computes a new igniter warm-up time for use during the next retry, as indicated at block 328. In particular, the controller 102 increases the current igniter warm-up time by a preset upward increment, e.g., six seconds. The new warm-up time is also stored. Using this new warm-up time, the start cycle, i.e., steps 304-316, are repeated, as indicated by block 330, and the controller 102 determines whether ignition was successful on this retry, as indicated by decision block 332. If it is, the controller 102 next determines whether the furnace has been started less than 250 consecutive times, as indicated at decision 334. If so, the controller uses the currently computed warm-up time during the next start cycle, as indicated at block 336, and checks for successful ignition, at decision block 332.

[0032] By virtue of block 326, the ignition control system 100 limits the igniter warm-up time to the preset maximum, which in this case is preferably 36 seconds. Accordingly, the warm-up time can range between a preset minimum of twelve seconds and a preset maximum of 36 seconds. With each successful start, the warm up time is reduced, preferably in three second increments, down to the preset minimum. And, with each failed start, the warm-up time is increased, preferably in three or six second increments, up to the preset maximum.

[0033] Returning to decision block 324 (FIG. 3B), if the failed ignition occurred after the first or second retry, the controller 102 computes a new warm-up by increasing the current warm-up time by the preset upward increment, e.g., three seconds, and repeats the start sequence, i.e., steps 304-316, using newly computed the warm-up time, as indicated at block 352. The controller 102 preferably maintains a counter that is incremented for each consecutive ignition failure. If ignition is still unsuccessful, the controller 102 determines whether the number of consecutive ignition failures is less than five, as indicated at decision block 338. If so, and the warm-up time is not at the preset maximum value, e.g., 36 seconds, as in block 354, then processing returns to decision block 324, as indicated by No arrow 355. Otherwise, the ignition sequence is repeated according to block 330. If the controller 102 is unable to start the furnace after five consecutive retries, it enters a lock-out state, as indicated by block 340. During the lock-out period, which may be on the order of 1 hour, the controller 102 is prevented from trying to start the furnace. At the end of the lock-out period, the controller returns to the wait state as represented by block 302 (FIG. 3A).

[0034] Referring to decision block 334, if the furnace has been successfully started 250 times or more consecutively, the controller 102 computes a new igniter warm-up time by decreasing the current warm-up time by the preset downward increment, e.g., three seconds, as indicated at block 322 (FIG. 3A). The controller 102 then returns to the wait state represented by block 302.

[0035]FIGS. 4A and 4B are a flow diagram of yet another furnace start cycle in accordance with the present invention. The steps corresponding to blocks 402-416 (FIG. 4A) correspond to the steps of blocks 202-216 of FIG. 2A described above. Based on the presence or absence of a flame at the expiration of the second preset time, the controller 102 makes a determination as to whether or not there has been a successful ignition of the burner 110, as indicated by decision block 418. In response to a successful ignition, the controller 102 decreases the igniter warm-up time for use during the next start cycle by a first preset downward increment, which, in this case, is preferably 24 seconds, as indicated by block 422. In other words, the microprocessor 104 computes a new igniter warm-up time as follows: 30−24=6 seconds, and stores this new warm-up time for use during the next start cycle of the furnace, as also indicated at block 422. Thus, in this embodiment, the warm-up time is rapidly reduced to a minimum warm-up time, e.g., six seconds, by the controller 102. The preset minimum is then used during the next start cycle, as indicated at block 423. Furthermore, this start cycle, including the six second warm-up time, is repeated, assuming ignition is successful, each time, as indicated by decision block 450 by which checks for successful ignition and Yes arrow 451 which loops processing back to block 423.

[0036] If, during the initial start cycle, ignition is unsuccessful, i.e., no flame is detected after waiting the second preset time following the opening of the gas valve 114, then processing moves from decision block 418 to block 424 (FIG. 4B). Here, the warm-up time is increased by a first preset upward increment, e.g., 24 seconds, and ignition is retried.

[0037] If ignition at the preset minimum igniter warm-up time, e.g., six seconds, is unsuccessful, then processing moves from decision block 450 (FIG. 4A) to block 426 (FIG. 4B) where the warm-up time is increased by a second preset upward increment, e.g., 12 seconds, and ignition is retried. At decision block 434, if there is successful ignition, then the warm-up time is decreased by a second preset downward increment, e.g., six seconds, at the next call for heat as shown at block 436. Otherwise, the warm-up time is increased by a third preset upward increment, e.g., six seconds, as shown at block 438, and ignition is retried. At decision block 444, if there is successful ignition after either increasing or decreasing the warm-up time as in blocks 436 and 438, then, if the warm-up time is at the preset minimum value, e.g., six seconds, as determined at decision block 446, the ignition sequence is repeated with the value of six seconds at the next call for heat as shown in block 464. If the warm-up time is not at the preset minimum value, it is preferably decreased by a third downward increment, e.g., three seconds, as shown in block 452, on the next call for heat. If, at decision block 444, ignition was not successful, the warm-up time is increased by a third upward increment, e.g., three seconds, and ignition is retried, as shown at block 454. Whether the warm-up time was increased or decreased by three seconds (blocks 454 and 452 respectively), if there is successful ignition, as shown by decision block 460, and if there have been no more than 251 consecutive successful ignitions, then the ignition sequence is repeated as indicated by block 464 with the current warm-up time at the next call for heat.

[0038] If, at decision block 460, ignition was unsuccessful, but there have been five or less consecutive retries as determined by decision block 466, and the warm-up time is at the preset maximum value, e.g., 54 seconds, as determined by decision block 462, and this is the first trial at the preset maximum value, as shown at decision block 440, then ignition is retried at a warm-up time at the preset maximum, as shown at block 442. If it is not the first trial at 54 seconds, then a lock-out occurs, as shown in block 432, followed by another attempt at ignition at a warm-up time of 30 seconds. The lock-out may extend for about one hour.

[0039] If, at decision block 462, the warm-up time has not reached the preset maximum, then the warm-up time is increased by the third preset upward increment, e.g., three seconds, and ignition is retried, as shown in block 454. If there have been more than five consecutive retries, as shown in decision block 466, then a lock-out occurs as in block 432, followed by another ignition attempt at block 402 at the initial warm-up time, e.g., 30 seconds.

[0040] If, at decision block 458, there are more than 250 consecutive successful ignitions, and if, at decision block 456, the warm-up time is at the preset minimum, e.g., six seconds, then the ignition sequence with the warm-up time at the preset minimum is repeated at the next call for heat, as shown in block 464. But if the warm-up time is greater than the preset minimum, e.g., greater than six seconds, but is not at a preset intermediate time, e.g., nine seconds, as shown at decision block 448, then the warm-up time is decreased by the second preset downward increment, e.g., six seconds, on the next call for heat as shown in block 436. If the warm-up time is at the intermediate time, the warm-up time is decreased to the preset minimum, e.g., six seconds, on the next call for heat, as shown in block 452.

[0041] It should be noted that each “successful ignition” decision block in FIG. 4B indicates that the ignition sequence represented by block 402-416 has been performed in response to a call for heat with the current warm-up time.

[0042] As in other embodiments, upon entering the lock-out state, the controller 102 may activate a diagnostic indicator, such as a set or row of LEDs, to notify service personnel of the failure or error condition. And, as in other embodiments, the maximum and minimum warm-up times and the increment or step values, e.g., 24, 12, six and three seconds, can be modified and still achieve the objectives of the present invention.

[0043]FIGS. 5A and 5B are a flow diagram of another start cycle in accordance with the present invention. The steps represented by blocks 502-516 correspond to the steps of blocks 202-216 of FIG. 2A described above. Based on the presence or absence of a flame at the expiration of the second preset time, the controller 102 makes a determination as to whether or not there has been a successful ignition of the burner 110, as indicated by decision block 518. In response to a successful ignition, the controller 102 decreases the igniter warm-up time for use during the next start cycle preferably by 24 seconds, as indicated by block 522. In other words, the microprocessor 104 computes a new igniter warm-up time as follows: 30−24=6 seconds, and stores this new warm-up time for use during the next start cycle of the furnace, as indicated at block 523. As with the start cycle of FIGS. 4A-4B, a minimum warm-up time, preferably of six seconds, is quickly established, and start cycles with this warm-up time are repeated, assuming ignition is successful each time.

[0044] If, during the initial start cycle, ignition is unsuccessful, i.e., no flame is detected after waiting the second preset time following the opening of the gas valve 114, then processing moves from decision block 518 to block 524 (FIG. 5B). Here, the warm-up time is increased preferably by 24 seconds, and ignition is retried.

[0045] If ignition is unsuccessful, then processing moves from decision block 550 to block 526 where warm-up time is increased preferably by 12 seconds and ignition is retried. At decision block 534, if there is successful ignition, then the warm-up time is decreased preferably by six seconds at the next call for heat, as shown at block 536. Otherwise, the warm-up time is increased preferably by six seconds, as shown at block 538, and ignition is retried. At decision block 544, if there is successful ignition after either increasing or decreasing the warm-up time, as in blocks 536 and 538, then, the warm-up time is decreased preferably by three seconds and the ignition sequence is repeated with the new value, e.g., six seconds, at the next call for heat. If ignition is not successful at decision block 544, the warm-up time is increased preferably by three seconds and ignition is retried, as shown in block 554.

[0046] Whether the warm-up time was increased or decreased (blocks 554 and 552 respectively), if there is successful ignition, as shown in decision block 560, and if there have been no more than a set number, which in this case is preferably 100, of consecutive successful ignitions, and the warm-up time is at the preset minimum, e.g., six seconds, as tested at decision block 556, then the ignition sequence is repeated, as in block 564, at the preset minimum warm-up time at the next call for heat. If the warm-up time is greater than the preset minimum, as tested as decision block 556, then the warm-up time is decreased preferably by three seconds, as shown at block 552, and that warm-up time is used at the next call for heat. If there have been more than 100 consecutive successful ignitions, as determined at decision block 558, then the current warm-up time is used on the next call for heat. If, at decision block 560, there has not been successful ignition, but there have been less than a set number, e.g., six, consecutive retries, as shown by decision block 566, and the warm-up time is at the preset maximum value, e.g., 54 seconds, as shown in decision block 562, then ignition is retried at the preset maximum warm-up time, as shown at block 542.

[0047] If, at decision block 562, the warm-up time has not reached the preset maximum, then the warm-up time is increased, as shown in block 554, preferably by three seconds and ignition is retried. If there have been more than five consecutive retries, as shown in decision block 566, then a lock-out preferably occurs as indicated at block 532, followed by another ignition attempt at block 502 preferably with a warm-up time at the initial value, e.g., 30 seconds.

[0048] It should be noted that each “successful ignition” decision block in FIG. 5B indicates that the ignition sequence 502-516 has been performed with the current warm-up time as a result of a call for heat.

[0049] Although the ignition control system 100 is preferably utilized with a furnace (not shown), those skilled in the art will recognize that system 100 may be used to control other devices or appliances, such as a dryer. It may also be used with propane as well as natural gas burners.

[0050] The foregoing description has been directed to specific embodiments of this invention. It will be apparent, however, that other variations and modifications may be made to the described embodiments, with the attainment of some or all of their advantages. Therefore, it is an object of the appended claims to cover all such variations and modifications as come within the true spirit and scope of the invention. 

What is claimed is:
 1. An ignition control system for use in attempting to start a fuel operated device, the ignition control system comprising: a burner; a fuel valve moveable between an open position and a closed position for selectively providing fuel to the burner; an igniter for igniting a fuel from the burner; a flame sensor configured and arranged to issue a signal indicative of the presence or absence of flame at the burner; and a controller operatively coupled to the igniter and the fuel valve, and in communicating relationship with the flame sensor, wherein the controller activates the igniter for a predetermined warm-up time, at the end of the predetermined warm-up time, the controller moves the fuel valve to the open position, after a first preset time following the opening of the fuel valve, the controller deactivates the igniter, after a second preset time following the opening of the fuel valve, the controller checks the flame sensor signal to see whether or not flame is present, thereby indicating a successful or an unsuccessful ignition, and if the ignition was successful, the controller decrements the igniter warm-up time during the next start and, if the ignition was unsuccessful, the controller increments the igniter warm-up time and tries to start the device again.
 2. The ignition control system of claim 1 wherein the igniter warm-up time is decremented to a minimum warm-up time and incremented to a maximum warm-up time.
 3. The ignition control system of claim 2 wherein the minimum warm-up time is one of approximately six and 12 seconds, and the maximum warm-up time is one of approximately 36 and 54 seconds.
 4. The ignition control system of claim 1 wherein the second preset time is approximately five seconds.
 5. The ignition control system of claim 1 wherein the controller includes a microprocessor and a programmable memory device.
 6. The ignition control system of claim 1 wherein the warm-up time is incremented and decremented in steps of one of approximately three, six, 12 and 24 seconds each.
 7. The ignition control system of claim 1 wherein, after an unsuccessful ignition followed by a successful retry attempt, the controller performs subsequent ignitions using the warm-up time of the successful retry attempt.
 8. The ignition control system of claim 7 wherein the controller performs a preset number of subsequently successful ignitions before decrementing the warm-up time.
 9. The ignition control system of claim 8 wherein the preset number is approximately
 250. 10. The ignition control system of claim 1 wherein the fuel is one of natural gas and propane.
 11. The ignition control system of claim 1 wherein the device is one of a furnace and an appliance.
 12. An method for use in attempting to start a fuel operated device having a burner, a fuel valve moveable between an open and a closed position for selectively providing fuel to the burner, an igniter for igniting a fuel from the burner, and a flame sensor configured and arranged to issue a signal indicative of the presence or absence of flame at the burner, the ignition method comprising the steps of: activating the igniter for a predetermined warm-up time; moving the fuel valve to the open position at the end of the predetermined warm-up time; deactivating the igniter after a first preset time following the opening of the fuel valve; checking the flame sensor signal to see whether or not flame is present, thereby indicating a successful or an unsuccessful ignition, after a second preset time following the opening of the fuel valve; if the ignition was successful, decrementing the igniter warm-up time during the next start; and if the ignition was unsuccessful, incrementing the igniter warm-up time and trying to start the device again.
 13. The method of claim 12 further comprising the steps of: blocking the igniter warm-up time from being decremented below a minimum warm-up time; and blocking the igniter warm-up time from being incremented above a maximum warm-up time.
 14. The method of claim 12 further comprising the step entering a lock-out state following a set number of unsuccessful ignition attempts whereby further attempts at ignition are suspended while in the lock-out state.
 15. The method of claim 13 further comprising the steps of: following a successful retry after an unsuccessful ignition attempt, utilizing the last computed igniter warm-up for one or more subsequent ignition attempts.
 16. The method of claim 15 further comprising the steps of: after an unsuccessful ignition attempt, determining whether there have been a fixed number of consecutive successful ignitions, and if so, decrementing the igniter warm-up time during the next ignition attempt.
 17. The method of claim 16 wherein the fixed number is approximately
 250. 18. The method of claim 12 wherein the igniter warm-up time is incremented and decremented in steps of one of approximately three, six, 12 and 24 seconds each.
 19. The method of claim 13 wherein the minimum warm-up time is one of approximately six and 12 seconds, and the maximum warm-up time is one of approximately 36 and 54 seconds. 